If you were to write "no one can help you to make sense of your existence" instead of "no one can help you make sense of your existence," you're actually writing the same sentence twice. "To make" is the verb, and the "to" can be omitted freely without changing the meaning. I read here that the "to" appears whenever the direct object precedes the indirect object, the direct object being "no one" and the indirect object being "you." If you were to switch these around so that the indirect object comes first, the sentence would be
This is the feeling of loneliness you get when you realize that you can be helped by no one to make sense of your existence.
U12-Forward said in their answer that "out" can be added to make your sentence sound more fluid. Meanwhile, I would add "own" myself.
No one can help you make sense of your own existence.
or, maybe change it up even further
You won't be able to find anyone to help you make sense of your own existence.
Besides the basic rules of sentence structure, (noun, verb, object, etc.) English gives you a lot of freedom in how you order the words and phrases that make up your sentence.
I have been editing a story on Wattpad for someone, and I found that they kept putting a prepositional phrase (of content) at the end of sentences instead of after the object that they were describing (a smile). As long as you don't do that, you'll be fine. Here's the sentence just in case I wasn't able to describe it well enough. :'D
He slept soundly, a smile on his face of content. <-- Wrong >:(
He slept soundly, a smile of content on his face. <-- Right :)